GFP labelled B. subtilis 3610 (NRS1473, green) exhibiting crowd movement around a tomato root (Solanum lycopersicum, red) growing in transparent soil saturated with a 78% percoll solution (6.6 mPa s-1). Filamentous flocks show the defined, multiple branching morphology associated with higher viscosity solutions. Images were collected at 30-minute intervals using a 2X objective. Time lapse covers a 10 hour period.